This invention relates to the delivery of radioisotopes to a disease-causing pathogen using a pathogen-targeting material conjugated to the radioisotope.
It is known to deliver cytotoxic radioisotopes to the nucleus of a tumor cell using a targeting protein or polypeptide conjugated with a radio-labeled nucleic acid-targeting small molecule. See, for example, U.S. Pat. No. 5,759,514. However, other than in the above referenced application, the use of radioisotopes to destroy disease-causing living pathogens such as bacteria or viruses has not heretofore been suggested.
Some strains of bacteria and viruses are very resistant to conventional drug therapy and are capable of killing or seriously debilitating the patient. Some strains are capable of mutating into a predominantly drug resistant form during the course of drug treatment, resulting in the death or debilitation of the patient. The widespread use of a particular drug treatment furthermore favors the genetic selection of strains which are resistant to that particular course of treatment. The presence of drug resistant strains of bacteria and viruses poses a growing world wide health threat.
A method for treating patients which have been infected with a drug-resistant pathogen would be very desirable. A technique for performing such treatment in a manner that minimizes the degree to which patients are exposed to a radioisotope would be even more desirable.
One embodiment of the invention provides a composition of matter suitable for use to treat disease in an extracorporal treatment technique. The composition comprises a conjugate of a living pathogen-targeting organic moiety coupled to a radioisotope which has a half-life of less than 100 days on a suitable support.
Another embodiment of the invention provides a method for treating an infectious disease caused by living blood-borne pathogens in a mammal. The process is conducted by obtaining antibodies from the mammal, replicating the antibodies to produce replicated antibodies, conjugating the replicated antibodies with a radioisotope which has a half-life of less than 100 days to produce a conjugate, fixing the conjugate to a conjugate support to form a supported conjugate, and passing the blood of the mammal into contact with the supported conjugate to bring the conjugate into contact with said living pathogens.
A further embodiment of the invention provides a method for treating an infectious disease caused by living blood-borne pathogens in a mammal. The method is carried out by identifying the blood-borne pathogens causing the infectious disease, selecting a supported conjugate comprising a particle support bearing an organic moiety which is chemically selective for attachment to said living pathogens and which is conjugated to a radioisotope which has a half-life of less than 100 days, flowing the blood of the mammal through a bed formed from particles of said supported conjugate, so that said blood-borne pathogens become associated with said radioisotope while in the bed, forming treated blood, and returning the treated blood to the mammal.
In one embodiment of the invention, there is provided a composition of matter comprising a living pathogen-targeting organic moiety which is conjugated to a radioisotope which has a half-life of less than 100 days and is deposited on a particulate substrate such as beads to facilitate an extracorporal treatment of the patient""s body fluid, such as blood.
Recent evidence has shown that radioisotopes which emit alpha, beta, or gamma radiation, and especially those of fairly short half-life and which emit Auger electrons during the decay process may be useful for inducing receptor cell specific cytotoxicity.
When a radioisotope decays by orbital electron capture or internal conversion, inner atomic shell vacancies are created in the residual atom. This highly excited atom attains a stable electronic configuration rapidly in a time scale of about 10xe2x88x9215 seconds via radioactive and non-radioactive transitions. In general, Auger, Coster-Kronig and super Coster-Kronig processes dominate the atomic vacancy cascades. As a result, numerous electrons are ejected from the atom and most of these Auger electrons have very low kinetic energies (about 20-500 eV) with extremely short ranges (a few nanometers) in water. Even though the energy carried by each of these electrons is only a small fraction of the total energy released in the decay process, their collective energy deposition is extremely high. Hence when the decays occur in the immediate vicinity of the critical biological molecules such as DNA, intracellular transmitters or any of the apoptotic cascade mechanisms, the biological effects to that cell are expected to be devastating.
Usually, radioisotopes used in accordance with the invention will have a half-life in the range of from about 1 to about 10 days. Preferably, the radioisotopes emit Auger electrons. Examples of suitable radioisotopes are Phosphorus 32, Copper 67, Gallium 67, Bromine 77, Yttrium 90, Technetium 99, Indium 111, Iodine 125, Iodine 131, Rhenium 186, Rhenium 188, Platinum 195, Bismuth 213, and Astatine 225. Of these, Copper 67, Yttrium 90, Indium 111, Rhenium 186, and Platinum 195 are preferred because these radioisotopes have distinct cytotoxic properties which may be exploited for therapy by the biologically directed targeting.
Compounds that are labeled with Auger electron emitters are most effective when the compound is internalized within or attached to the cell in a manner capable of activating apoptosis. Auger electrons provide very high-energy emissions but do so over a very short distance or action, which is less than 10-20 microns. This allows for an Auger emitting radioisotope to bring a high energy destructive force into areas to cause critical DNA strand damage (mitochondrial or nuclear). This, in turn activates the mechanism of apoptosis. Therefore, for a radioisotope-ligand to be a particularly desirable therapeutic agent, the compound must have a high cell to be destroyed-to background tissue ratio, a high therapeutic ratio and pharmacokinetic biodistribution profiles that optimize receptor binding, ligand internalization and cellular retention. The effects, therefore, of Auger electron emitters depend upon their cellular and sub-cellular location, which is governed, in turn, by the chemical form of the molecular agent (bioactive substance) to which the radioisotope has been attached.
Generally speaking, the living pathogen-targeting organic moiety is in the form of an antiviral, antifungal or an antibacterial antibody, although fragments of such antibodies or antibiotics which function to selectively carry the radioisotope into or onto a targeted pathogen are also considered suitable. Viruses, fungi bacteria, or prions may be selected as targets by appropriate selection of the organic moiety. Usually, the organic moiety has a surface chemistry which associates with a surface chemistry of the targeted pathogen. More preferably, the organic moiety has a surface chemistry to associate with a unique surface chemistry of the targeted pathogen.
Circulating antibodies normally recognize an antigen in the serum or tissue fluids and, furthermore, there are five identifiable classes: IgG, IgA, IgM, IgD and IgE. In addition to antigen binding, all antibodies exert other specific biological activities. The antigen-binding site is usually one in which there is a Fc fragment and two-antigen binding FAB fragments. X-ray crystallography and electron microscopy has provided the structural and biochemical organization of these moieties. Disulfide bonds predominate in cross-linking many of these domains. The primary function of any antibody is to bind any recognizable antigen. Recently, libraries of human specific antibody variable genes have been constructed for recombinant filamentous phages, which display the antibodies on their surface, and it is possible to select from high affinity antibodies for any chosen cell surface antigens from these libraries
Phage antibodies that bind to a particular antigen may be separated from non-binding phage antibodies by antigen selection and the bound antibodies are recovered by elution. Repeated rounds of selection can isolate antigen-binding phages that were present at the start of the process at frequencies of less than one in a billion.
One technique of producing a homologous population of antibodies of known antigen specificity, are known as hybridomas that are derived from a single B cells and are called monoclonal antibodies. Another technique for producing antibody molecules is named phage antibody or phage libraries. In this case, gene segments encoding antigen-binding variable or V domains of antibodies are fused to genes encoding the coat protein of a bacteriophage. A collection of recombinant phage, each displaying a different antigen-binding domain on its surface is known as a phage display library. Each phage isolated in this way win produce a monoclonal antigen-binding particle analogous to a monoclonal antibody. Genes encoding the antigen-binding site, which are unique to each phage, can then be recovered from the phage DNA and used to construct genes for a complete antibody molecule by joining them to gene segments that encode the invariant parts of an antibody. When these reconstructed antibody genes are introduced into a suitable host cell line, the transferred cells secrete antibodies with all of the desirable characteristics on monoclonal antibodies that are produced from hybridomas.
The antibody binds stably to its antigen as the antibodies recognize the surface features of the native folded protein antigen and the antibody molecules can thus be used to locate their target molecules accurately in single cells or in tissue sections.